Fiber glass is currently produced from glass fiber bushings which typically are controlled electrically to maintain the temperature of the glass contained in the bushing within a desired range. Maintenance of a desired glass temperature insures uniform viscosity of the molten glass in a bushing and thus uniform filament formation as fibers are drawn from the molten glass as it exits through the bushing orifices, all other conditions being equal. The bushings themselves are precious metal containers typically having 4 sides and a bottom and are generally open at the top. The bushings are provided with a plurality of orifices in the bottom which normally have tips depending therefrom through which the molten glass contained in the bushing flows to form the glass fibers. Bushings are heated by applying current to leads located at each end of the bushing, the leads being connected to the secondary winding of a suitably sized power transformer. The current is increased or decreased by connecting a power pack to the power transformer and altering the output of the power pack by feeding signals to it from a controller that is fed signals from thermocouples attached to the bushing that monitor its operating temperatures continuously.
While the present systems utilized to control bushing temperatures appear adequate in that they do represent the measurements taken from the bushing, they are not actually adequate because they do not necessarily represent the real temperature of the bushing orifice or tip plate. This is so because conventional measurements made do not usually represent true averages of the bushing tip plate temperature. In assignee's copending application Ser. No. 941,236, filed Dec. 12, 1986, a process is described which gives a more accurate measurement of bushing tip plate temperatures. This process requires in part, measurements from the tip plate of the bushing alone or in addition to the normal measurements taken at the bushing sides.
In accomplishing these measurements of the bushing tip plate, it is an important consideration that the thermocouple junction attached to the bottom or tip plate of the bushing be protected and be as flat as possible with respect to the tip plate of the bushing to which it is attached. Molten glass movement in the bushing caused by the molten glass flowing from the forehearth to the bushing and glass currents contained within the bushing itself should not be capable of disturbing the electrical connection of the thermocouple junction and wires with the bushing tip plate. Further, the junction should be able to be welded to the bushing tip plate with a minimum of difficulty.